(4) A small glass or glazed porcelain combustion tube D, filled with
copper oxide and heated by two or three bunsen fan flames, with the object
of transforming into carbon dioxide the small amounts of carbon monoxide
or hydrocarbons which may be formed in the reaction.
(5) A U-tube (E) with ground stoppers and filled with phosphoric anhy-
dride to retain the moisture in the gas.1
(6) Two U-tubes (F, F), with ground stoppers, for absorbing the carbon
dioxide ; the left branch and half of the right are charged with granular
soda lime (granules 1-1-5 mm.) covered with loose glass wool plugs, the
rest of the right limb being filled with phosphoric anhydride also capped
with a glass wool plug. One of these tubes is usually sufficient to fix all
the carbon dioxide evolved, and may be used for several determinations,
the other serving as control.2
(7) A U-tube (G) containing phosphoric anhydride and a wash-bottle
(H) with cone, caustic soda solution to protect the absorption tubes from
atmospheric moisture and carbon dioxide.
(8) An aspirator (/) to regulate the gas current.
Procedure. When the apparatus has been fitted together as shown
and the joints made air-tight, 35 c.c. of the chromic acid solution, 150 c.c.
of the copper sulphate solution and 200 c.c. of cone, sulphuric acid (D 1-84)
are introduced into the flask by raising the ground glass plug of the funnel
i ', to destroy any organic matter present, the mixture is boiled for about
half an hour, a gentle current of air being drawn through the apparatus
and the glass or porcelain tube heated. During this preliminary operation
it is useless to insert the series of U-tubes.
Meanwhile the soda lime tubes are weighed and also the sample, which
should be in powder or fine filings.3
1 The phosphoric anhydride may be replaced by calcium chloride, provided that
this has been recently saturated with carbon dioxide to neutralise alkalinity due to the
presence of lime.
2 These two tubes may be replaced by Geissler bulbs filled with 30% caustic potash
3 The sample may be weighed either in a small glass tube with a foot and poured
into the flask through a funnel (Fig. g, b) with a long, wide stem, or in a small platinum
bucket which is suspended in the liquid in the flask by a platinum wire attached to a
suitable hook fused on to the bottom of the condenser (Fig. g, a), or in a small thin-walled
glass tube which is introduced directly into the flask.phite, also insoluble